Superheterodyne receiver with local oscillator operating at intermediate frequency for simultaneously monitoring plural channels



Apnl 29, 1958 H. BRETT 2,832,885

SUPERHETERODYNE RECEIVER WITHLOCAL OSCILLATOR OPERATING AT INTERMEDIATE FREQUENCY FOR SIMULTANEOUSLY MONITORING PLURAL CHANNELS Filed Oct. so, 1956 FlG.l

INVENTOR.

HERBERT BRETT B Y y Unite States Patent SUPERHETERODYNE REEIVER WITH LOCAL OSCILLATOR OPERATING AT INTERIWEDIATE FREQUENCY FGR SIMULTANEOUSLY MONI- TORING PLURAL CHANNELS Herbert Brett, Fair Haven, N. J., assignor to the United States of America as represented by the Secretary of The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

The invention relates to improvements in microwave radio receivers and more particularly to means for increasing the sensitivity thereof.

In accordance with the invention, the receiver comprises a dual diode mixer, one diode of which is normally excited by a locally generated wave having a frequency which is low relative to that of the incoming wave, said frequency being of the order of the intermediate frequency. In the absence of a signal, the locally generated wave is shorted out in the mixer circuit so that it is prevented from reaching the intermediate frequency amplitier. When a microwave signal is impressed upon the diodes, it is modulated by the low frequency wave, and the resultant modulated wave is demodulated by the other diode to derive the intermediate frequency signal component, which is, in turn, applied to and amplified by the I. F. amplifier and detected in the usual manner.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken inv conjunction with the accompanying drawing, in which: Figure l is a schematic circuit diagram of the invention; and

Figure 2 is a cross section taken along lines 2-2 of Figure 1.

In Figure 1 of the drawing, there is shown a cross sectional view of a waveguide 10. The section is taken through the axis of the waveguide in a direction parallel to the narrow walls thereof. The mouth of the waveguide 12 is flared outwardly to form a horn-shaped openmg.

The waveguide is dimensioned to pass the high frequency band of interest e. g., 8000-12,000 megacycles. It may be tunable to any frequency within the band by means of aslidable plunger 14. The waveguide may, of course, be of the broad band type responsive to the entire band of frequencies to be received.

In the absence of a microwave signal in .the waveguide, the output of I. F.- oscillator 24 which is applied to diode 18 is shorted out by rod 16, since the latter is short relative to the I. F; wavelength and its impedance thereto is negligible. Hence no I. F. current reaches amplifier 28. When an incoming microwave signal is impressed on the waveguide considerable voltage drop occurs through rod 16 and detectors 18 and 20, since the rod is long relative to the wavelength of the microwave signal, and hence it offers considerable impedance thereto. The incoming signal is therefore modulated by the I. F. current in diode 18. The resultant modulated current is demodulated by diode 20, and the resultant I. F. signal is amplified by I. F. amplifier 28 and applied to detector 30. Any modulation component on the received microwave frequency signal will be derived at the output of detector 30. The resultant signal can then be further amplified and indicated in the usual manner.

The above-described system is relatively simple and has been found to provide improved signal to noise ratio.

'le there has beendescribed what is at present considered a preferred embodiment of the'invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A microwave receiver comprising a rectangularwaveguide, means for propagating received microwaves in said waveguide, a local oscillator for generating an intermediate frequency wave which is low relative to the received waves, a first circuit within said waveguide, said 7 microwaves are modulated by said intermediate frequency wave, an output circuit including a demodulator in said waveguide connected to said first circuit for demodulating the modulated received waves to derive said intermediate frequency, and a utilization circuit tuned to said intermediate frequency connected to said output circuit.

2. A receiver as set forth in claim 1, wherein said first circuit comprises a metal bar extending centrally of said j received waves and low to said intermediate frequency,

Extending between the narrow walls of the waveguide is a metal supporting rod 16, on opposite sides of which are located a pair of crystal diodes l8 and 2t), and having their cathodes connected to said rod. The diodes may be of any suitable type such as silicon.

By means of a concentric cable 22, the anode of diode 18 is connected to an oscillator 24 operating at a relatively low intermediate frequency, such as 30-60 megacycles. The anode of the other diode 20 is connected through a concentric cable 26 to an amplifier 28 tuned to the same intermediate frequency. The output of amplifier 28 is applied to an amplitude modulation detector 30. The detected signal may be further amplified and reproduced in the usual manner.

circuit comprises a metal bar connected between the narrower walls of said waveguide, said diodes being positioned at the center of said bar on opposite sides thereof and each having a similar electrode connectedto said 3 center, the other electrode of one diode being connected 2,605,399 to said local oscillator, and the other electrode of the ,7 other diode being connected to said output circuit. 2,761,061 2,773,979

7 References Cited in the file of this patent 5 UNITED STATES PATENTS 2,576,481 Rodwin- Nov. 27, 1951 Pound July 29, 1952 Ienks July 19, 1955 Mattern Aug. 28, 1956 Chatterton Dec. 11, 1956 

